1. Field of the Invention
The present invention relates to an apparatus and method for non-invasively measuring a blood glucose concentration in the human body, and more particularly, to a non-invasive blood glucose sensors using a magneto-resonance absorption method and measurement methods thereof.
2. Description of the Related Art
Diabetics have suddenly increased in number due to lack of physical activities and changes of eating habits. The deaths caused by diabetes in 2001 in Korea are 23.8 people per hundred thousand people, stand fourth in the death causes, and increased about two times 11.8 people per hundred thousand people in 1990. Individual diabetics must measure blood glucose by themselves due to the increase in number, i.e., self-monitoring of blood glucose is required. Self-monitoring of blood glucose is an important component of modern therapy for diabetes and offers information about blood glucose levels at many times points to enable maintenance of a more constant glucose levels in everyday life. The self-monitoring of blood glucose is suggested to be taken at least three or four times a day. However, it is reported that only 18% of diabetics periodically measure blood glucose even in the U.S.A in a good social welfare. The negligence of the measurement of blood glucose is due to current invasive-type glucose meters which require blood samples directly taken from the body. Periodical tests by the invasive method not only give pain or uncomfortable feelings during taking bloods but also impose mental and economic burdens with considerable costs of consumable accessories necessary for taking bloods.
Devices for non-invasive measurement of blood glucose have been developed to solve such pain and displeasure during taking of blood, to reduce cost of diagnostic strips and to smoothly perform self-measurement of the blood glucose. As non-invasive measurement methods of blood glucose, methods of using an analysis of a absorption spectrum in an infrared zone and a method of using impedance spectroscopy in a band of tens to hundreds MHz have been studied.
Also, non-invasive blood glucose measurement methods using a nuclear magneto-resonance spectroscopy principle are disclosed in U.S. Pat. Nos. 4,875,486, 5,685,300, and 6,163,154. In such measurement methods, a correlation between a resonance peak (or area) by a water component and a resonance peak (or area) by a glucose component on a nuclear magneto-resonance spectrum of blood or the tissue of the human body is used or a degree of a chemical shift by the glucose component on the spectrum is used to measure blood glucose, the chemical shift being caused by variations in a blood glucose concentration. However, due to the effect of the nuclear magneto-resonance spectrum by the water component, it is substantially very difficult to sense a variation in the magnitude of the resonance peak or a very small variation in the chemical shift by the glucose component. Thus, non-invasive blood glucose sensors using such measurement methods are not developed yet.
There is reported a magneto-resonance absorption method (O. C. Esicov and E. A. Protasov, “Magneto-resonance method of measurement of spin-lattice time by using absorption signal,” Scientific session MEPhI Conference, Vol. 4, pp. 35, 2003.) by which an absorption signal in a time domain occurring during nuclear magneto-resonance is measured to analyze components in a material. There is reported a glucose concentration measurement method using an electromagnetic field (E. A. Protasov, O. C. Esicov and E. C. Karpova, “Glucose concentration measurements in the human blood by NMR method,” Scientific session MEPhI Conference, Vol. 5, pp. 3, 2003) by which a correlation between a blood glucose level in blood or the human body and a magneto-resonance spin-lattice relaxation time measured by a magneto-resonance absorption method is defined to determine a blood glucose concentration in blood or the human body using the correlation.
An external magnetic field must be highly uniform in order to secure the measurement precision in blood glucose measurement using a nuclear magneto-resonance principle. However, the essential uniformity of the external magnetic field may not be secured in existing blood glucose sensors using an electromagnetic field due to the unstableness of a supplied voltage. Thus, it is unreasonable that the existing blood glucose sensors are commonly used. For reference, according to the existing blood glucose measurement results, the uniformity of an external magnetic field having the strength between 0.15 T and 0.35 T must be within a range of 2.5×10−4 T to detect variations in a spin-lattice relaxation time of a finger or a blood sample caused by variations in a blood glucose concentration. Also, blood glucose sensors using an electromagnetic field are constructed considerably heavy and big in order to form an external magnetic field having a desired strength and thus are not suitable as home non-invasive blood glucose sensors.
Russian Pat. No. 33235 discloses a non-invasive blood glucose sensor using permanent magnets to non-invasively measure blood glucose using a magneto-resonance absorption method. In this non-invasive blood glucose sensor, a pair of permanent magnets is used to form a constant magnetic field so as to remove variations in the magnetic field caused by an unstable power supply. However, it is difficult to obtain the required uniformity of the magnetic field with only the pair of permanent magnets. The uniformity of the magnetic field basically depends on the perfection of the permanent magnets. Thus, the irregular arrangement of foreign bodies, bubbles, or contents in a material of the magnets causes a disturbance of local magnetization, the disturbance distorting the magnetic field. The non-invasive blood glucose sensor is a single closed shell, internal elements of which are connected to form a magnetic circuit. Since the accurate arrangement of the internal elements of the shell is difficult due to the single closed structure, the internal elements are disarranged. Thus, the distribution of the magnetic field is non-uniform. Absorption pulses of a detected signal are distorted or diffused by the non-uniform distribution of the magnetic field. Thus, it is difficult to accurately detect an absorption signal and measure a nuclear magneto-resonance spin-lattice relaxation time. As a result, the precision or accuracy of the determination of a blood glucose level in the human body is deteriorated.